SEASONAL-CHANGES IN MICROBIAL BIOMASS AND ACTIVITY IN LEAF-LITTER LAYERS OF BEECH (FAGUS-SYLVATICA) FORESTS ON A BASALT-LIMESTONE GRADIENT

Microbial biomass (SIR), basal respiration and specific respiration (q O(2)) were investigated in three different beech leaf litter layers (u pper, intermediate, lower). The study sites were located on the slope of a hill forming a gradient in parent rock from basalt (upper part of the hill) to limestone (lower part of the hill) with an intermediate site in between. Microbial parameters were investigated in each season in 1993. Microbial biomass remained very constant throughout the year in each of the layers while basal respiration and specific respiratio n declined during summer but increased in November. This inrease, whic h occured after shedding of leaves of beech trees, is ascribed to leac hing of carbon resources and nutrients from fresh beech leaf litter. M icrobial biomass, basal respiration and specific respiration declined strongly with litter depth. Presumably, this decline reflects depletio n of available carbon resources during litter decomposition. In genera l, microbial biomass in beech leaf litter layers of the study site (16 mg C g(-1) dry mass, overall mean pooled for layer and site) exceeded that reported previously for the upper mineral soil layer by a factor of about 12. The respective factor for basal respiration (154 mu l O( 2)h(-1) g(-1) dry mass, overall mean pooled for layer and site) is cal culated to be 34. The gradient in parent rock did not consistently aff ect microbial parameters in the litter layers. Substrate-induced respi ration (SIR) is assumed to be a good measure for determination of micr obial biomass in beech leaf materials. The usefulness of the specific respiration as a parameter for microbial carbon use efficiency is disc ussed.